1. Field of the Invention
The present invention relates to a magnetic recording device, and more particularly, to a thin film magnetic head suitable for use in a magnetic disk device.
2. Description of the Prior Art
A recording density of the magnetic recording devices has been remarkably increased and still intensively contrived to further increase by many workers in various fields. The recording density has been increasing in a rate of becoming about twice in 2.5 to 3 years and plays an important role in the external storage devices for the information retrieval society. An important part which is essential to the increase the recording density of magnetic disk devices is a thin film magnetic head. Comparing with ferrite type bulk magnetic heads which have been employed for the magnetic heads in the magnetic disk devices over the years, the thin film magnetic heads can easily be provided with narrow channelings and are capable of exhibiting a high ratio of signal to noise (S/N) in the high-frequency range of several megahertz to several tens megahertz. Therefore, further development of the thin film magnetic heads has been increasingly demanded.
Recording and reproducing properties of the thin film magnetic heads depend extensively on magnetic properties of the magnetic films. For the thin film magnetic heads to be used in the high frequency range, they must have a higher permeability than that of ordinary magnetic films in the high frequency range. As an example of the magnetic films having a high permeability in the high frequency range, permalloy which is an alloy of nickel and iron has been known. Permalloy thin films have been employed as magnetic films in the thin film magnetic heads as has been well known in the art. There have been known two main techniques, i.e., plating process and sputtering process for producing the permalloy thin film for use in the thin film magnetic heads. On the other hand, an instability of reproducing output of the thin film magnetic heads is attributed to the magnetic films having a non-uniform distribution of the composition thereof and a varying composition owing to compositional variation from lot to lot in the production of the magnetic films. It has been evident that the sputtering process which can provide a uniform composition throughout the magnetic films and a good reproducibility in composition to every lot in the process is superior and advantageous in commercial production as compared with the plating process.